1. Field of the Invention
The present invention relates to a connecting material in the form of a liquid or paste which contains a thermosetting resin.
2. Description of the Related Art
A widely used method for mounting bare IC chips on wiring circuit boards is a flip-chip method which uses a connecting material that contains a thermosetting resin and a latent curing agent. Connecting materials such as anisotropic conductive adhesive pastes (ACP) and non-conducting adhesive pastes (NCP) in liquid- or paste-form have been used at normal temperatures in such mounting methods, with said materials being able to reduce tact time in the mounting step and to be applied on wiring circuit boards with a known dispenser for materials which are in the form of a paste or liquid, which requires a relatively low cost for introduction of facilities.
However, when using connecting materials in the form of a liquid or paste to mount bare IC chips on wiring circuit boards, gasification of the volatile component of the connecting material, air being trapped during the coating process, gasification of any moisture contained in the board and other such reasons cause voids to form in the connecting material layer which has been sandwiched between the wiring circuit board and the bare IC chip, and removing these voids from the system causes the melt viscosity of the connecting material to become too low during the heat and pressure application processes. Accordingly, if the voids are not removed from the connecting material layer after the hot curing process, then the resistance values following the reflow and aging processes will rise to a level unsuitable in practical application, and in certain cases the bare IC chip will float or peel off, leading to poor continuity.
Methods have been developed to try to rid the connecting material layer of voids, e.g., carrying out the heat and pressure application processes in two stages, or controlling the profile of the conditions for heat/pressure application, such as slowing down the rate of heating, but their efficacy has been less than satisfactory.